Scarlett Johansson's ass-kicking Avenger gets a stand-alone movie at last in Black Widow. No longer just a sidekick to Iron Man or Captain America, Johansson gives a cracking performance as Natasha Romanoff, a whip-smart, Russian-trained killing machine. Now she's on the side of the American Avengers, and begins a mission to destroy the Russians' Red Room programme, which trains and brainwashes young girls, including herself, to become Black Widow killers and spies. Natasha is joined — and almost immediately upstaged — by her little sister Yelena, played by British actress Florence Pugh with oomph, wit and often hilarious, childlike enthusiasm. Scarlett Johansson's ass-kicking Avenger gets a stand-alone movie at last in Black Widow.